DSB-COFDM RF signals have been used several years for over-the-air broadcasting of DTV in accordance with the DVB-T and DVB-T2 Standards for Digital Video Broadcasting in several countries other than the United States of America and Canada. DSB-COFDM RF signals are being broadcast in the United States of America in accordance with an ATSC 3.0 Standard developed by the Advanced Television Systems Committee, an industry-wide consortium of DTV broadcasters, manufacturers of DTV transmitter apparatus and manufacturers of DTV receiver apparatus.
Prior-art receivers for DSB COFDM RF signals, such as receivers for DTV broadcasting, have folded the frequency spectrum in half by synchrodyne to baseband before discrete Fourier transform (DFT) and demapping quadrature amplitude-modulation (QAM) of COFDM signal subcarriers, thus to improve signal-to-noise ratio (SNR) by 6 dB.
U.S. Pat. No. 7,236,548 titled “Bit level diversity combining for COFDM system” issued 26 Jun. 2007 to Monisha Ghosh, Joseph P. Meehan and Xuemei Ouyang described a novel way of combining of multiple-input/multiple-output DSB-COFDM television signals after they are each synchrodyned to baseband. These synchrodyning procedures fold the frequency spectra of the COFDM signals in half to halve the number of spectral component terms obtained from subsequent DFT procedures performed on each COFDM signal. These spectral component terms are quadrature-amplitude modulation (QAM) symbols in regard to each COFDM subcarrier. U.S. Pat. No. 7,236,548 concerned the signal-to-noise ratio (SNR) obtained during reception via an additive white Gaussian noise (AWGN) channel. A 6 DB improvement in SNR is obtained by maximal-ratio combining corresponding QAM symbols obtained from the respective DFT procedures performed on each of a pair of COFDM signals of equal strength, such maximal-ratio combining being performed before demapping the QAM symbols resulting from such combining. U.S. Pat. No. 7,236,548 advocates an alternative procedure in which corresponding QAM symbols obtained from the respective DFT procedures performed on each of a pair of COFDM signals of equal strength are demapped individually, followed by maximal-ratio combining of the corresponding demapping results being performed at bit level. This alternative procedure improves the effective SNR for reception via an AWGN channel by an additional 2.5 dB or so over the 6 dB expected from the doubling of received power.
No evidence is known suggesting that the U.S. Pat. No. 7,236,548 technique of maximal-ratio combining of the corresponding demapping results being performed at bit level was ever previously applied to the lower and upper sidebands of a single DSB-OFDM signal. No evidence is known that indicates specifically how to weight the corresponding results of demapping corresponding QAM symbols from the lower and upper sidebands of a single DSB-OFDM signal during diversity combining of them.